This research will be conducted primarily in Brazil as an extension of NIH grants # R0l CA 50385 and R0l HL60712-0l. Overweight (BMI (Body Mass Index) 25.0-29.9) and obesity (BMI greater than or equal to 30 kg/m2) now affect more than 40 percent of adult Brazilians. Women at reproductive age are particularly at risk of obesity and a 70 percent increase in the prevalence was observed in the last two decades in Brazil. Increasing fat intake does not appear to explain this trend, whereas a steady decline in the consumption of beans has been shown for the whole country. Many studies have demonstrated changes in blood glucose levels due to the intake of specific carbohydrate foods, as measured by glycemic index (GI). An exceptionally low blood glucose response was associated with beans and it has been suggested that the consumption of low-GI diets may: 1) decrease hunger/ increase satiation; 2) reduce lipogenesis. In a nonrandomized follow-up of children attending a program of obesity treatment, children assigned to a low GI diet had a decrease in BMI greater than the high GI group. There are no long term clinical trials of weight loss or prevention of weight gain comparing low with high GI diets. However, a dietary pattern identified through factor analysis in a survey in the city of Rio de Janeiro, Brazil, that represents mainly rice and bean intake was associated with lower risk of obesity. The purpose of this study is to compare in Brazilian women the effectiveness of encouraging them to eat two different dietary patterns (low vs. high GI), with equal macronutrient composition, on weight control over the course of 18 months. The low GI dietary pattern will be heavily based on the traditional rice and beans combination. The comparison group will be encouraged to eat a diet with the same amount of macronutrients, but closer to a Western diet. Both diets are realistic prescriptions of foods consumed by Brazilians.Specifically, this study will compare changes in weight (main outcome), food intake, blood chemistries and hunger/satiation in 206 adult women at reproductive age, with BMI of 23-27 kg/m2, randomized to either one of the diets after 4-week run-in period eating a high GI diet.